Objective    To explore the effect of isoflurane on the expression of choline acetyltransferase (ChAT) in the hippocampus and spatial learning and memory function in aged rats.      Methods    A total of 54 20-month Sprague-Dawley male rats

were randomly divided into 3 groups with 18 rats each group. Group A (control group) received a breath of 30% oxygen and air mixed gas for 6 h; Group B (Single inhalation of isoflurane group) were anesthetized with 1.2% isoflurane

30% oxygen and air mixed gas for 6 h; Group C (Repeated inhalation of isoflurane group) were anesthetized with 1.2% isoflurane

30% oxygen and air mixed gas 2 h every day for 3 d. Five rats were randomly selected from each group for the arterial blood gas analysis in the course of treatment. Another five rats randomly selected from each group were killed and their hippocampus were immediately isolated for detection of ChAT expression by immunohistochemical assay and RT-PCR in 24 h after treatment. The spatial learning and memory function of 24 remained rates was assessed with Morris water-maze test form 1 d to 6 d after treatment.      Results    The expression levels of mRNA and protein of ChAT in the hippocampus was significantly lower in group B and group C than group A (P0.05). At day 2

3

4 and 5 after treatment

the escape latency in group B and group C was observed significantly longer compared with that of group A (P0.05). Learning and memory curve was shift right in group B and group C

and turned to be stable at the 4th day but at the 3rd day in group A. The results of Morris water-maze test showed that the frequency of crossing the original platform and the time consumption of staying the original platform quadrant was lower in group B and group C than those in group A (P0.05). No significant differences was found between group B and group C (P0.05).      Conclusion    Isoflurane reduces the short-term spatial learning and memory function in aged rats and this effects may be induced by the decrease of ChAT expression in the hippocampus.